As an example of a conventional art using a distributed power source, such as fuel cells, a solar power generation system, or the like, upon interruption of electric service, there has been known a technique disclosed in JP,A 9-121457. According to this patent document, once a large-scale interruption of electric service has been caused by, for example, a fall-down of an electric power pylon for a high-voltage trunk transmission line, a control center commands and controls distributed power sources to supply power so that the total of a suppliable electric energy from the distributed power sources becomes equal to an unsuppliable electric energy. On the other hand, as facilities for supplying power only during interruption of the service, batteries (principally lead storage batteries) are used for emergency power generators or emergency power sources in hospitals, large-scale buildings, and the like.
If the deregulation of electric power industry moves forward into the future, cost competition would suppress the capital investment in power stations, power transmission/transformation facilities, and the like, resulting in shortages of the amounts of power generation and transmission. This would incur a situation in which a stable power supply becomes unattainable. For example, as in the California power crisis, which caused a serious trouble in 2001, periodical and long-term interruptions of electric service might occur.
However, utilizing a distributed power source using the conventional art as countermeasures against a long-term service interruption occurring under such a situation includes the following problems.
Firstly, the guideline on power supply from a distributed power source is not well-defined, so that there is no other choice but to supply power to an indefinite number of loads. However, because the power generation capacity of the distributed power source is small, power can be supplied to only loads within a limited range. Therefore, it cannot be known until an interruption of electric service actually occurs, to which loads power can be supplied. This is a very risky situation when seen from the load side (power demand side).
Secondly, within a power supply network with a distributed power source, power supply/demand balance controlling means consists of only the control of the power generation output of the distributed power source and the opening/closing of loads, that is, there is provided only limited balance control means. As a result, if the supply/demand of power gets out of balance even to a minimum extent, loads are to be shut off one after another. This is also a very unstable situation when seen from the load side (power demand side).
Thirdly, many of distributed power sources to be introduced in the future are considered to be owned not by electric utilities (power providers), but by private companies. In this case, an electric utility cannot take the liberty of manipulating a power source owned by a private company. However, it is difficult for the owner itself of a private power source to execute the control of power supply/demand balance in place of the electric utility.
Also, the battery, serving as an emergency power generator or emergency power source, is intended to supply power to private facilities upon interruption of electric service, and does not supply power to a load other than the private facilities. This has a problem that a load without an emergency power generator cannot receive a power supply upon interruption of the service.